<!doctype html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <title>Readline Node.js v0.8.12 Manual &amp; Documentation</title>
  <link rel="stylesheet" href="assets/style.css">
  <link rel="stylesheet" href="assets/sh.css">
  <link rel="canonical" href="http://nodejs.org/api/readline.html">
</head>
<body class="alt apidoc" id="api-section-readline">
    <div id="intro" class="interior">
        <a href="/" title="Go back to the home page">
            <img id="logo" src="http://nodejs.org/images/logo-light.png" alt="node.js">
        </a>
    </div>
    <div id="content" class="clearfix">
        <div id="column2" class="interior">
            <ul>
                <li><a href="/" class="home">Home</a></li>
                <li><a href="/download/" class="download">Download</a></li>
                <li><a href="/about/" class="about">About</a></li>
                <li><a href="http://search.npmjs.org/" class="npm">npm Registry</a></li>
                <li><a href="http://nodejs.org/api/" class="docs current">Docs</a></li>
                <li><a href="http://blog.nodejs.org" class="blog">Blog</a></li>
                <li><a href="/community/" class="community">Community</a></li>
                <li><a href="/logos/" class="logos">Logos</a></li>
                <li><a href="http://jobs.nodejs.org/" class="jobs">Jobs</a></li>
            </ul>
            <p class="twitter"><a href="http://twitter.com/nodejs">@nodejs</a></p>
        </div>

        <div id="column1" class="interior">
          <header>
            <h1>Node.js v0.8.12 Manual &amp; Documentation</h1>
            <div id="gtoc">
              <p>
                <a href="index.html" name="toc">Index</a> |
                <a href="all.html">View on single page</a> |
                <a href="readline.json">View as JSON</a>
              </p>
            </div>
            <hr>
          </header>

          <div id="toc">
            <h2>Table of Contents</h2>
            <ul>
<li><a href="#readline_readline">Readline</a><ul>
<li><a href="#readline_readline_createinterface_options">readline.createInterface(options)</a></li>
<li><a href="#readline_class_interface">Class: Interface</a><ul>
<li><a href="#readline_rl_setprompt_prompt_length">rl.setPrompt(prompt, length)</a></li>
<li><a href="#readline_rl_prompt_preservecursor">rl.prompt([preserveCursor])</a></li>
<li><a href="#readline_rl_question_query_callback">rl.question(query, callback)</a></li>
<li><a href="#readline_rl_pause">rl.pause()</a></li>
<li><a href="#readline_rl_resume">rl.resume()</a></li>
<li><a href="#readline_rl_close">rl.close()</a></li>
<li><a href="#readline_rl_write_data_key">rl.write(data, [key])</a></li>
</ul>
</li>
<li><a href="#readline_events">Events</a><ul>
<li><a href="#readline_event_line">Event: &#39;line&#39;</a></li>
<li><a href="#readline_event_pause">Event: &#39;pause&#39;</a></li>
<li><a href="#readline_event_resume">Event: &#39;resume&#39;</a></li>
<li><a href="#readline_event_close">Event: &#39;close&#39;</a></li>
<li><a href="#readline_event_sigint">Event: &#39;SIGINT&#39;</a></li>
<li><a href="#readline_event_sigtstp">Event: &#39;SIGTSTP&#39;</a></li>
<li><a href="#readline_event_sigcont">Event: &#39;SIGCONT&#39;</a></li>
</ul>
</li>
<li><a href="#readline_example_tiny_cli">Example: Tiny CLI</a></li>
</ul>
</li>
</ul>

          </div>

          <div id="apicontent">
            <h1>Readline<span><a class="mark" href="#readline_readline" id="readline_readline">#</a></span></h1>
<pre><code>Stability: 2 - Unstable</code></pre>
<p>To use this module, do <code>require(&#39;readline&#39;)</code>. Readline allows reading of a
stream (such as <code>process.stdin</code>) on a line-by-line basis.

</p>
<p>Note that once you&#39;ve invoked this module, your node program will not
terminate until you&#39;ve closed the interface. Here&#39;s how to allow your
program to gracefully exit:

</p>
<pre><code>var readline = require(&#39;readline&#39;);

var rl = readline.createInterface({
  input: process.stdin,
  output: process.stdout
});

rl.question(&quot;What do you think of node.js? &quot;, function(answer) {
  // TODO: Log the answer in a database
  console.log(&quot;Thank you for your valuable feedback:&quot;, answer);

  rl.close();
});</code></pre>
<h2>readline.createInterface(options)<span><a class="mark" href="#readline_readline_createinterface_options" id="readline_readline_createinterface_options">#</a></span></h2>
<p>Creates a readline <code>Interface</code> instance. Accepts an &quot;options&quot; Object that takes
the following values:

</p>
<ul>
<li><p><code>input</code> - the readable stream to listen to (Required).</p>
</li>
<li><p><code>output</code> - the writable stream to write readline data to (Required).</p>
</li>
<li><p><code>completer</code> - an optional function that is used for Tab autocompletion. See
below for an example of using this.</p>
</li>
<li><p><code>terminal</code> - pass <code>true</code> if the <code>input</code> and <code>output</code> streams should be
treated like a TTY, and have ANSI/VT100 escape codes written to it.
Defaults to checking <code>isTTY</code> on the <code>output</code> stream upon instantiation.</p>
</li>
</ul>
<p>The <code>completer</code> function is given a the current line entered by the user, and
is supposed to return an Array with 2 entries:

</p>
<ol>
<li><p>An Array with matching entries for the completion.</p>
</li>
<li><p>The substring that was used for the matching.</p>
</li>
</ol>
<p>Which ends up looking something like:
<code>[[substr1, substr2, ...], originalsubstring]</code>.

</p>
<p>Example:

</p>
<pre><code>function completer(line) {
  var completions = &#39;.help .error .exit .quit .q&#39;.split(&#39; &#39;)
  var hits = completions.filter(function(c) { return c.indexOf(line) == 0 })
  // show all completions if none found
  return [hits.length ? hits : completions, line]
}</code></pre>
<p>Also <code>completer</code> can be run in async mode if it accepts two arguments:

</p>
<pre><code>function completer(linePartial, callback) {
  callback(null, [[&#39;123&#39;], linePartial]);
}</code></pre>
<p><code>createInterface</code> is commonly used with <code>process.stdin</code> and
<code>process.stdout</code> in order to accept user input:

</p>
<pre><code>var readline = require(&#39;readline&#39;);
var rl = readline.createInterface({
  input: process.stdin,
  output: process.stdout
});</code></pre>
<p>Once you have a readline instance, you most commonly listen for the
<code>&quot;line&quot;</code> event.

</p>
<p>If <code>terminal</code> is <code>true</code> for this instance then the <code>output</code> stream will get
the best compatibility if it defines an <code>output.columns</code> property, and fires
a <code>&quot;resize&quot;</code> event on the <code>output</code> if/when the columns ever change
(<code>process.stdout</code> does this automatically when it is a TTY).

</p>
<h2>Class: Interface<span><a class="mark" href="#readline_class_interface" id="readline_class_interface">#</a></span></h2>
<p>The class that represents a readline interface with an input and output
stream.

</p>
<h3>rl.setPrompt(prompt, length)<span><a class="mark" href="#readline_rl_setprompt_prompt_length" id="readline_rl_setprompt_prompt_length">#</a></span></h3>
<p>Sets the prompt, for example when you run <code>node</code> on the command line, you see
<code>&gt; </code>, which is node&#39;s prompt.

</p>
<h3>rl.prompt([preserveCursor])<span><a class="mark" href="#readline_rl_prompt_preservecursor" id="readline_rl_prompt_preservecursor">#</a></span></h3>
<p>Readies readline for input from the user, putting the current <code>setPrompt</code>
options on a new line, giving the user a new spot to write. Set <code>preserveCursor</code>
to <code>true</code> to prevent the cursor placement being reset to <code>0</code>.

</p>
<p>This will also resume the <code>input</code> stream used with <code>createInterface</code> if it has
been paused.

</p>
<h3>rl.question(query, callback)<span><a class="mark" href="#readline_rl_question_query_callback" id="readline_rl_question_query_callback">#</a></span></h3>
<p>Prepends the prompt with <code>query</code> and invokes <code>callback</code> with the user&#39;s
response. Displays the query to the user, and then invokes <code>callback</code>
with the user&#39;s response after it has been typed.

</p>
<p>This will also resume the <code>input</code> stream used with <code>createInterface</code> if
it has been paused.

</p>
<p>Example usage:

</p>
<pre><code>interface.question(&#39;What is your favorite food?&#39;, function(answer) {
  console.log(&#39;Oh, so your favorite food is &#39; + answer);
});</code></pre>
<h3>rl.pause()<span><a class="mark" href="#readline_rl_pause" id="readline_rl_pause">#</a></span></h3>
<p>Pauses the readline <code>input</code> stream, allowing it to be resumed later if needed.

</p>
<h3>rl.resume()<span><a class="mark" href="#readline_rl_resume" id="readline_rl_resume">#</a></span></h3>
<p>Resumes the readline <code>input</code> stream.

</p>
<h3>rl.close()<span><a class="mark" href="#readline_rl_close" id="readline_rl_close">#</a></span></h3>
<p>Closes the <code>Interface</code> instance, relinquishing control on the <code>input</code> and
<code>output</code> streams. The &quot;close&quot; event will also be emitted.

</p>
<h3>rl.write(data, [key])<span><a class="mark" href="#readline_rl_write_data_key" id="readline_rl_write_data_key">#</a></span></h3>
<p>Writes <code>data</code> to <code>output</code> stream. <code>key</code> is an object literal to represent a key
sequence; available if the terminal is a TTY.

</p>
<p>This will also resume the <code>input</code> stream if it has been paused.

</p>
<p>Example:

</p>
<pre><code>rl.write(&#39;Delete me!&#39;);
// Simulate ctrl+u to delete the line written previously
rl.write(null, {ctrl: true, name: &#39;u&#39;});</code></pre>
<h2>Events<span><a class="mark" href="#readline_events" id="readline_events">#</a></span></h2>
<h3>Event: &#39;line&#39;<span><a class="mark" href="#readline_event_line" id="readline_event_line">#</a></span></h3>
<p><code>function (line) {}</code>

</p>
<p>Emitted whenever the <code>input</code> stream receives a <code>\n</code>, usually received when the
user hits enter, or return. This is a good hook to listen for user input.

</p>
<p>Example of listening for <code>line</code>:

</p>
<pre><code>rl.on(&#39;line&#39;, function (cmd) {
  console.log(&#39;You just typed: &#39;+cmd);
});</code></pre>
<h3>Event: &#39;pause&#39;<span><a class="mark" href="#readline_event_pause" id="readline_event_pause">#</a></span></h3>
<p><code>function () {}</code>

</p>
<p>Emitted whenever the <code>input</code> stream is paused.

</p>
<p>Also emitted whenever the <code>input</code> stream is not paused and receives the
<code>SIGCONT</code> event. (See events <code>SIGTSTP</code> and <code>SIGCONT</code>)

</p>
<p>Example of listening for <code>pause</code>:

</p>
<pre><code>rl.on(&#39;pause&#39;, function() {
  console.log(&#39;Readline paused.&#39;);
});</code></pre>
<h3>Event: &#39;resume&#39;<span><a class="mark" href="#readline_event_resume" id="readline_event_resume">#</a></span></h3>
<p><code>function () {}</code>

</p>
<p>Emitted whenever the <code>input</code> stream is resumed.

</p>
<p>Example of listening for <code>resume</code>:

</p>
<pre><code>rl.on(&#39;resume&#39;, function() {
  console.log(&#39;Readline resumed.&#39;);
});</code></pre>
<h3>Event: &#39;close&#39;<span><a class="mark" href="#readline_event_close" id="readline_event_close">#</a></span></h3>
<p><code>function () {}</code>

</p>
<p>Emitted when <code>close()</code> is called.

</p>
<p>Also emitted when the <code>input</code> stream receives its &quot;end&quot; event. The <code>Interface</code>
instance should be considered &quot;finished&quot; once this is emitted. For example, when
the <code>input</code> stream receives <code>^D</code>, respectively known as <code>EOT</code>.

</p>
<p>This event is also called if there is no <code>SIGINT</code> event listener present when
the <code>input</code> stream receives a <code>^C</code>, respectively known as <code>SIGINT</code>.

</p>
<h3>Event: &#39;SIGINT&#39;<span><a class="mark" href="#readline_event_sigint" id="readline_event_sigint">#</a></span></h3>
<p><code>function () {}</code>

</p>
<p>Emitted whenever the <code>input</code> stream receives a <code>^C</code>, respectively known as
<code>SIGINT</code>. If there is no <code>SIGINT</code> event listener present when the <code>input</code>
stream receives a <code>SIGINT</code>, <code>pause</code> will be triggered.

</p>
<p>Example of listening for <code>SIGINT</code>:

</p>
<pre><code>rl.on(&#39;SIGINT&#39;, function() {
  rl.question(&#39;Are you sure you want to exit?&#39;, function(answer) {
    if (answer.match(/^y(es)?$/i)) rl.pause();
  });
});</code></pre>
<h3>Event: &#39;SIGTSTP&#39;<span><a class="mark" href="#readline_event_sigtstp" id="readline_event_sigtstp">#</a></span></h3>
<p><code>function () {}</code>

</p>
<p><strong>This does not work on Windows.</strong>

</p>
<p>Emitted whenever the <code>input</code> stream receives a <code>^Z</code>, respectively known as
<code>SIGTSTP</code>. If there is no <code>SIGTSTP</code> event listener present when the <code>input</code>
stream receives a <code>SIGTSTP</code>, the program will be sent to the background.

</p>
<p>When the program is resumed with <code>fg</code>, the <code>pause</code> and <code>SIGCONT</code> events will be
emitted. You can use either to resume the stream.

</p>
<p>The <code>pause</code> and <code>SIGCONT</code> events will not be triggered if the stream was paused
before the program was sent to the background.

</p>
<p>Example of listening for <code>SIGTSTP</code>:

</p>
<pre><code>rl.on(&#39;SIGTSTP&#39;, function() {
  // This will override SIGTSTP and prevent the program from going to the
  // background.
  console.log(&#39;Caught SIGTSTP.&#39;);
});</code></pre>
<h3>Event: &#39;SIGCONT&#39;<span><a class="mark" href="#readline_event_sigcont" id="readline_event_sigcont">#</a></span></h3>
<p><code>function () {}</code>

</p>
<p><strong>This does not work on Windows.</strong>

</p>
<p>Emitted whenever the <code>input</code> stream is sent to the background with <code>^Z</code>,
respectively known as <code>SIGTSTP</code>, and then continued with <code>fg(1)</code>. This event
only emits if the stream was not paused before sending the program to the
background.

</p>
<p>Example of listening for <code>SIGCONT</code>:

</p>
<pre><code>rl.on(&#39;SIGCONT&#39;, function() {
  // `prompt` will automatically resume the stream
  rl.prompt();
});</code></pre>
<h2>Example: Tiny CLI<span><a class="mark" href="#readline_example_tiny_cli" id="readline_example_tiny_cli">#</a></span></h2>
<p>Here&#39;s an example of how to use all these together to craft a tiny command
line interface:

</p>
<pre><code>var readline = require(&#39;readline&#39;),
    rl = readline.createInterface(process.stdin, process.stdout);

rl.setPrompt(&#39;OHAI&gt; &#39;);
rl.prompt();

rl.on(&#39;line&#39;, function(line) {
  switch(line.trim()) {
    case &#39;hello&#39;:
      console.log(&#39;world!&#39;);
      break;
    default:
      console.log(&#39;Say what? I might have heard `&#39; + line.trim() + &#39;`&#39;);
      break;
  }
  rl.prompt();
}).on(&#39;close&#39;, function() {
  console.log(&#39;Have a great day!&#39;);
  process.exit(0);
});</code></pre>

          </div>
        </div>
    </div>
    <div id="footer">
        <ul class="clearfix">
            <li><a href="/">Node.js</a></li>
            <li><a href="/download/">Download</a></li>
            <li><a href="/about/">About</a></li>
            <li><a href="http://search.npmjs.org/">npm Registry</a></li>
            <li><a href="http://nodejs.org/api/">Docs</a></li>
            <li><a href="http://blog.nodejs.org">Blog</a></li>
            <li><a href="/community/">Community</a></li>
            <li><a href="/logos/">Logos</a></li>
            <li><a href="http://jobs.nodejs.org/">Jobs</a></li>
            <li><a href="http://twitter.com/nodejs" class="twitter">@nodejs</a></li>
        </ul>

        <p>Copyright <a href="http://joyent.com/">Joyent, Inc</a>, Node.js is a <a href="/trademark-policy.pdf">trademark</a> of Joyent, Inc. View <a href="https://raw.github.com/joyent/node/v0.8.12/LICENSE">license</a>.</p>
    </div>

  <script src="../sh_main.js"></script>
  <script src="../sh_javascript.min.js"></script>
  <script>highlight(undefined, undefined, 'pre');</script>
  <script>
    window._gaq = [['_setAccount', 'UA-10874194-2'], ['_trackPageview']];
    (function(d, t) {
      var g = d.createElement(t),
          s = d.getElementsByTagName(t)[0];
      g.src = '//www.google-analytics.com/ga.js';
      s.parentNode.insertBefore(g, s);
    }(document, 'script'));
  </script>
</body>
</html>

